Exercise 1 High-Voltage Disconnecting Switches and Circuit ... · PDF filefunctions and operation of high-voltage disconnecting switches and circuit ... High-voltage disconnecting

© Festo Didactic 20528-00 11

When you have completed this exercise, you will be able to describe the functions and operation of high-voltage disconnecting switches and circuit breakers used in electric power substations.

The Discussion of this exercise covers the following points:

Introduction

High-voltage disconnecting switchesFunctions of the disconnecting switch. Circuit diagram symbols of the disconnecting switch. Disconnecting switch operation. Rating of high-voltage disconnecting switches. Cost.

High-voltage circuit breakersFunctions of the circuit breaker. Circuit diagram symbols of the circuit breaker. Circuit breaker operation. Arc extinction in a high-voltage circuit breaker. Operating mechanism of the circuit breaker. Rating of high-voltage circuit breakers. Cost.

Introduction

The switchgear used in any electric power substation mainly consists of high-voltage disconnecting switches and circuit breakers, as mentioned earlier in this manual. The rest of this discussion explains the role and operation of the high-voltage disconnecting switches and circuit breakers used in electric power substations.

High-voltage disconnecting switches

This section of the discussion is separated into several subsections, with each subsection dealing with a particular aspect of the high-voltage disconnecting switches used in electric power substations.

Functions of the disconnecting switch

A high-voltage disconnecting switch is a mechanical switching device that can open or close a circuit under no-load while providing a specified isolating distance when in the open state. This isolation distance also serves the purpose of providing a clear indication of the disconnecting switch state to maintenance personnel.

High-Voltage Disconnecting Switches and Circuit Breakers

Exercise 1

EXERCISE OBJECTIVE

DISCUSSION OUTLINE

DISCUSSION

Disconnecting switches are

sometimes referred to as

disconnectors or isolators.

Exercise 1 – High-Voltage Disconnecting Switches and Circuit Breakers Discussion

12 © Festo Didactic 20528-00

A disconnecting switch is also able to carry circuit current up to the specified full-load current value as well as to carry, for a certain specified time, current (up to the specified maximum current value) in a circuit operating under abnormal conditions like a short-circuit. In general, a disconnecting switch is also able to open or close a circuit when the current is of relatively low value (e.g., the magnetizing current of a power transformer operating without load). Finally, a disconnecting switch can make or break a circuit operating at significant load current values, provided that the voltage across its contacts is maintained close to zero when it is either opened or closed.

In conclusion, disconnecting switches are not designed to make or break any significant load current in a circuit. However, disconnecting switches in the open state provide a means of isolating de-energized circuits prior to a repair or maintenance of equipment in order to ensure the safety of the maintenance personnel.

a A disconnecting switch is not designed to make or break a circuit operating under significant load current conditions because it has no provision to quickly suppress the electric arc that develops across its contacts when it is either opened or closed. The power in such an electric arc (product of the arc current times the voltage across the disconnecting switch contacts) is generally sufficient to cause the disconnecting switch contacts to heat up considerably and rapidly. Consequently, damage to the disconnecting switch contacts are likely to occur when severe arcing occurs, i.e., when the disconnecting switch is used to open or close a circuit operating under significant load current conditions.

Figure 7. The switchgear used in any electric power substation mainly consists of high-voltage disconnecting switches and circuit breakers (© Siemens AG 2014, all rights reserved).



Circuit diagram symbols of the disconnecting switch

Figure 8 shows the symbols that are commonly used to represent a single-pole disconnecting switch in circuit diagrams.

Figure 8. Circuit diagram symbols for the single-pole disconnecting switch.

Figure 9 shows symbols that are commonly used to represent a three-pole disconnecting switch in circuit diagrams. Three-pole disconnecting switches are commonly used in electric power substations.

Figure 9. Circuit diagram symbols for the three-pole disconnecting switch.

Throughout this manual, the symbols shown in Figure 8a and Figure 9a are used. These symbols represent non-motorized disconnecting switches. Such disconnecting switches can only be operated manually. Motor-operated disconnecting switches are also available to allow remote control. Figure 10 shows symbols used to represent a single-pole, motor-operated disconnecting switch and a three-pole, motor-operated disconnecting switch in circuit diagrams.

Figure 10. Circuit diagram symbols for the single-pole, motor-operated disconnecting switch and the three-pole, motor-operated disconnecting switch.

(a) (b)

(a) (b)

(a) Single-pole (b) Three-pole

M M



Figure 11. High-voltage, single-pole, motor-operated disconnecting switch. This particular disconnecting switch is of the center-break type and is opened or closed by rotating the two arms at the top of the unit in the horizontal plan. (© Siemens AG 2014, all rights reserved).

Disconnecting switch operation

Figure 12 shows a simplified diagram of a high-voltage, three-pole, motor-operated disconnecting switch typical of those used in modern electric power substations. It consists of a set of three main contacts, auxiliary contacts, an operating mechanism, and a control system.

The operation of the motor-operated disconnecting switch is very simple. The control system can receive commands from several different sources (SCADA system, local electrical controls, and remote control signal inputs). The control system either opens or closes (depending on the command received) the main contacts of the disconnecting switch by making an electric motor in the operating mechanism rotate clockwise or counterclockwise. Opening or closing a motor-operated disconnecting switch is an operation that takes a certain amount of time, generally between 5 s and 15 s. The operating mechanism mainly consists of an array of shafts, gears, levers, and cams that are arranged in a way that makes the operation of the disconnecting switch as reliable as possible. Note that the disconnecting switch shown in the diagram above can also be opened or



closed by manually actuating the operating mechanism of the switch using a crank handle. In this case, the time required to open or close the disconnecting switch depends on the effort of the operator.

The auxiliary contacts, which are actuated by cams in the operating mechanism, indicate the state (open, in transit, or closed) of the main contacts of the disconnecting switch with absolute reliability. The design of the cams used in the operating mechanism determines the relationship between the three possible states of the disconnecting switch and the states of the auxiliary contacts.

Figure 12. Simplified diagram of a high-voltage, three-pole, motor-operated disconnecting switch.

A single set of auxiliary con-

tacts (i.e., one normally-open

contact and one normally-

closed contact) is shown in

the diagram of Figure 12.

However, several sets are

generally available on actual

disconnecting switches. Main

contactsAuxiliary contacts

Open (O) Close (I) Open (O) Close (I)

Remote control signal inputs

Local electrical controls(e.g., push buttons)

Open (O) and close (I)commands fromSCADA system

Local mechanical control (e.g., crank handle)

Comm. port (RS-485 or Ethernet)

Control system

Operating mechanism

Close (I)Open (O)



Figure 13 shows an example of the relationship between the three possible states of the disconnecting switch and the states of the auxiliary contacts. It is commonly used in Europe.

a Whenever a disconnecting switch receives an open command, the main contacts first separate from each other (electric contact breaks almost immediately), and then continue to move away from each other until the specified isolating distance is reached. However, the disconnecting switch is considered to be in the open state only once its main contacts have reached the specified isolating distance (generally 5 to 15 s after the main contacts have separated from each other).

In this situation, the normally-open (NO) auxiliary contact is open and the normally-closed (NC) auxiliary contact is closed when the main contacts of the disconnecting switch are open. Conversely, the normally-open (NO) auxiliary contact is closed and the normally-closed (NC) auxiliary contact is open when the main contacts of the disconnecting switch are closed. Also, both auxiliary contacts are closed when the disconnecting switch is passing from the open state to the closed state or vice versa (in-transit state).

Figure 13. Relationship between the three possible states of the disconnecting switch and the states of the auxiliary contacts (European practice).

State of the normally-closed auxiliary contact

State of the normally-open auxiliary contact

State of the disconnecting switch

main contacts

Close command

Closed

Closed

Closed Closed

Open

Open

Open

Open

Open

In transit In transit

Open command



Figure 14 shows another example of the relationship between the three possible states of the disconnecting switch and the states of the auxiliary contacts. It is commonly used in North America.

In this situation, the normally-open (NO) auxiliary contact is open and the normally-closed (NC) auxiliary contact is closed when the main contacts of the disconnecting switch are open. Conversely, the normally-open (NO) auxiliary contact is closed and the normally-closed (NC) auxiliary contact is open when the main contacts of the disconnecting switch are closed. So far, this is identical to the European practice described in the previous example. However, both auxiliary contacts are open (instead of being closed as in the European practice) when the disconnecting switch is passing from the open state to the closed state or vice versa (in-transit state).

Figure 14. Relationship between the three possible states of the disconnecting switch and the states of the auxiliary contacts (North American practice).

The auxiliary contacts can be used to control pilot lights indicating the disconnecting switch state (open, in transit, or close), confirm the disconnecting switch state to the SCADA system (via the control system), and confirm the disconnecting switch state to protection systems.

The control system can receive commands from several different sources, as mentioned earlier. The open (O) and close (I) commands from the SCADA system are generally used for operational and maintenance purposes. The open (O) and close (I) commands from the local electrical controls are mainly used for maintenance purposes. Finally, open (O) and close (I) commands, often coming from protection equipment, can sometimes be received at the remote control signal inputs.

State of the normally-closed auxiliary contact

State of the normally-open auxiliary contact

State of the disconnecting switch

main contacts

Close command

Closed

Closed

ClosedClosed

Open

Open

Open

Open

Open

In transit In transit

Open command



Rating of high-voltage disconnecting switches

Table 1 provides the main specifications of a typical high-voltage disconnecting switch designed to be used in electric power substations.

Table 1. Specifications of a 300 kV disconnecting switch.

Parameter description Value

Rated voltage 300 kV

Rated power-frequency withstand voltage (to ground and between phases)

380 kV

Rated power-frequency withstand voltage (across the isolating distance)

435 kV

Rated lightning-impulse withstand voltage (to ground and between phases)

1050 kV

Rated lightning-impulse withstand voltage (across the isolating distance)

1050 kV

Maximum, rated normal current 4 kA

Maximum, rated peak withstand current 160 kA

Maximum, rated short-time withstand current 63 kA

Rated duration of short-circuit 0.33 s

Rated frequency 50 Hz or 60 Hz

Each parameter in Table 1 is briefly described below:

Rated voltage: Voltage at which the disconnecting switch is designed to operate (300 kV in this case).

Rated power-frequency withstand voltage (to ground and between phases): Indicates that the disconnecting switch can sustain voltage at the rated power frequency (either between a line and ground or between two lines) up to a value of 380 kV.

Rated power-frequency withstand voltage (across the isolating distance): Indicates that the air gap between the main contacts of the disconnecting switch when fully open can sustain voltage at the rated power frequency up to a value of 435 kV.

Rated lightning-impulse withstand voltage (to ground and between phases): Indicates that the disconnecting switch can sustain overvoltage caused by lightning (either between a line and ground or between two lines) up to a value of 1050 kV.

Rated lightning-impulse withstand voltage (across the isolating distance): Indicates that the air gap between the main contacts of the disconnecting switch when fully open can sustain overvoltage caused by lightning up to a value of 1050 kV.



Maximum, rated normal current: Maximum current (4 kA in this case) which the disconnecting switch can carry continuously.

Maximum, rated peak withstand current: Maximum current (160 kA in this case) which the disconnecting switch can carry.

Maximum, rated short-time withstand current: Maximum current (63 kA in this case) which the disconnecting switch can carry for a short time (less than 0.33 s in this case).

Rated duration of short-circuit: Time during which the disconnecting switch can sustain short-circuit currents (0.33 s in this case).

Rated frequency: Frequency at which the disconnecting switch is designed to operate (50 Hz or 60 Hz in this case).

Cost

High-voltage disconnecting switches are much less expensive than high-voltage circuit breakers. This is largely due to their very limited ability to switch current in energized circuits.

High-voltage circuit breakers

This section of the discussion is separated into several subsections, each subsection dealing with a particular aspect of the high-voltage circuit breakers used in electric power substations.

Figure 15. High-voltage, three-pole circuit breaker in an air-insulated electric power substation. The three large horizontal components atop the vertical post insulators are the three interrupter units of the circuit breaker (© Siemens AG 2014, all rights reserved).



Functions of the circuit breaker

A high-voltage circuit breaker is a mechanical switching device that can make, carry, and break current in a circuit operating under normal conditions (e.g., when full load current flows in a circuit). This function of the circuit breaker allows the path through which power flows in an electric power substation to be interrupted or modified for normal operation and maintenance purposes.

A high-voltage circuit breaker can also make, carry (for a specified time), and break current (up to a specified short-circuit current value) in a circuit operating under abnormal conditions like a short-circuit. This function of the circuit breaker allows faulty equipment in an electric power substation to be quickly disconnected to protect other equipment in the substation. Contrary to fuses, a circuit breaker can be reset quickly after operation (e.g., after a short-circuit has tripped the circuit breaker), thereby allowing the supply of power to be restored in a short time.

Circuit diagram symbols of the circuit breaker

Figure 16 shows the symbols that are commonly used to represent a single-pole circuit breaker in circuit diagrams.

Figure 16. Circuit diagram symbols for the single-pole circuit breaker.

Figure 17 shows symbols that are commonly used to represent a three-pole circuit breaker in circuit diagrams. Three-pole circuit breakers are commonly used in electric power substations.

Figure 17. Circuit diagram symbols for the three-pole circuit breaker.

Throughout this manual, the symbols shown in Figure 16a and Figure 17a are used.

(a) (b) (c)

(a) (b)



Circuit breaker operation

Figure 18 shows a simplified diagram of a high-voltage, three-pole circuit breaker typical of those used in modern electric power substations. It consists of three interrupter units (i.e., the main contacts of the circuit breaker), auxiliary contacts, an operating mechanism, and a control system.

Figure 18. Simplified diagram of a high-voltage, three-pole circuit breaker.

The operation of the high-voltage circuit breaker is very simple. The control system can receive commands from several different sources (SCADA system, local controls, and remote control signal inputs). The control system makes the interrupter units open or close (depending on the command received) via the operating mechanism. The operating mechanism provides the energy necessary to ensure fast and reliable actuation of the interrupter units and auxiliary contacts of the circuit breaker. The operating mechanism of the circuit breaker is described in detail later in this discussion.

A single set of auxiliary

contacts (i.e., one normally-

open contact and one nor-

mally-closed contact) is

shown in the diagram of

Figure 18, although several

sets are generally available

on actual circuit breakers.

Interrupter units (main contacts)

Auxiliary contacts

Operating mechanism

Open (O) Close (I) Open (O) Close (I)

Remote control signal inputs

Local electrical controls(e.g., push buttons)

Open (O) and close (I)commands fromSCADA system

Comm. port (RS-485 or Ethernet)

Control system

Close (I) Open (O)



The auxiliary contacts indicate the state (open or close) of the interrupter units (i.e., the state of the circuit breaker main contacts). When the interrupter units are open, i.e., when the main contacts of the circuit breaker are open, the normally-open (NO) auxiliary contact is open and the normally-closed (NC) auxiliary contact is closed. Conversely, when the interrupter units are closed, i.e., when the main contacts of the circuit breaker are closed, the normally-open (NO) auxiliary contact is closed and the normally-closed (NC) auxiliary contact is open. The auxiliary contacts can be used to control pilot lights indicating the circuit breaker state (open or close), confirm the circuit breaker state to the SCADA system (via the control system), and confirm the circuit breaker state to protection systems.

The control system can receive commands from several different sources as mentioned earlier. The open (O) and close (I) commands from the SCADA system are generally used for operational and maintenance purposes. The open (O) and close (I) commands from the local controls are mainly used for maintenance purposes. Finally, the open (O) and close (I) commands received at the remote control signal inputs are used for protection purposes.

Arc extinction in a high-voltage circuit breaker

A high-voltage circuit breaker can make, carry, and break current in a circuit operating under normal conditions as well as abnormal conditions like a short-circuit. The task of breaking current in a circuit operating under abnormal conditions is the most demanding because an arc forms at the circuit breaker main contacts when they begin to open and current continues to flow in the circuit as long as the arc is present. This arc must be extinguished as quickly as possible to interrupt the circuit current as soon as possible and limit the amount of heat produced by the arc, thereby preventing damage to the protected equipment and the circuit breaker main contacts. Therefore, a means of ensuring rapid arc extinction is an essential feature of any high-voltage circuit breaker.

Various media are used for arc extinction in high-voltage circuit breakers: oil, air, sulphur hexafluoride (SF6), and vacuum. The medium used for arc extinction is generally used to classify high-voltage circuit breakers. This leads to the following classes of high-voltage circuit breakers:

Oil circuit breakers

Air-blast circuit breakers

Sulphur hexafluoride (SF6) circuit breakers

Vacuum circuit breakers



Figure 19. Example of an oil circuit breaker (photo courtesy of Open Electrical).

Figure 20. Example of a sulphur hexafluoride (SF6) circuit breaker (© Siemens AG 2014, all rights reserved).



Figure 21 illustrates how arc extinction is achieved in an SF6 circuit breaker.

When the circuit breaker is closed (Figure 21a), current flows through the contact carrier (1), main contact (4), contact cylinder (5), and base (6) of each interrupter unit. When the circuit breaker starts to open (Figure 21b), the main contact (4) first separates from the contact cylinder (5) but current continues to flow through each interrupter unit via the arcing contact (3) which is still closed at that instant. A little later in the course of the circuit breaker opening (Figure 21c), the arcing contact (3) opens and an arc appears at the arcing contact. At the same time, downward motion of the contact cylinder (5) compresses SF6 gas located in the base (6). This causes SF6 gas to flow through the contact cylinder (5) and the nozzle (2) to the arcing contact (3), thereby extinguishing the arc.

When interrupting a high short-circuit current, the SF6 gas in each interrupter unit is heated up considerably at the arcing contact (3) due to the energy of the arc. This causes the pressure in the contact cylinder (5) to increase and more SF6 gas to flow at the arcing contact (3) through the nozzle (2), thereby extinguishing the arc. In other words, the arc energy is used to help extinguish the arc, and thus, contributes to the interruption of the fault current. Consequently, this reduces the amount of energy that the operating mechanism of the circuit breaker has to provide for the arc extinction and current interruption.

Figure 21. Arc extinction in an SF6 circuit breaker (© Siemens AG 2014, all rights reserved).

(b) Opening: main contact in open position

(c) Opening: arcing contact in open position

(d) Open position (a) Closed position

Contactcarrier

Nozzle

Arcingcontact

Maincontact

Contactcylinder

Base



Operating mechanism of the circuit breaker

Any high-voltage circuit breaker used in electric power substations requires an operating mechanism that is fast (to notably limit arcing at opening), reliable, and virtually maintenance free. Two types of operating mechanism are commonly used: stored-energy spring mechanisms and electro-pneumatic or electro-hydraulic operating mechanisms.

A stored-energy spring mechanism is an arrangement of rods, shafts, levers, cams, gears, and springs designed to ensure fast and reliable operation of a high-voltage circuit breaker. Such an operating mechanism requires energy to be stored in a primary spring (also referred to as the closing spring) before the circuit breaker can be operated. The amount of energy stored in the closing spring of the mechanism, though limited, is sufficient to allow one closing-opening cycle of the circuit breaker. When the circuit breaker receives a command to close, part of the energy stored in the closing spring is used to close the circuit breaker contacts and the remainder of the stored energy is transferred to a secondary spring (also referred to as the opening spring), i.e., the remaining stored energy compresses the opening spring. Transferring some of the energy stored in the closing spring to the opening spring at closure of the circuit breaker ensures that the circuit breaker contacts can then be opened without delay if required.

A stored-energy spring mechanism needs to be recharged (i.e., the closing spring needs to be compressed again) after any closure of the circuit breaker. Energy storage is generally achieved using an electric motor coupled to the operating mechanism via a set of gears and takes more or less time depending on the design of the mechanism. Therefore, the circuit breaker can no longer be closed for a short period of time after the energy stored in the closing spring of the mechanism has been released. A long (e.g., 30 s) energy-storage time (closing spring recompression time) after closure of the circuit breaker is a limitation that can be problematic in certain situations, such as when multiple attempts to reclose a circuit are required after a fault.

An electro-pneumatic or electro-hydraulic operating mechanism uses either a pneumatic cylinder or a hydraulic cylinder to ensure fast and reliable operation of a high-voltage circuit breaker. Actuation of the cylinder in either of these two mechanisms is through a valve that is controlled electromagnetically. Because the supply of air or oil is continuously regulated in such operating mechanisms, the circuit breaker can perform successive closing-opening cycles without having to wait for energy to be stored in the mechanism between each cycle. This is an advantage that the electro-pneumatic and electro-hydraulic operating mechanisms have over most stored-energy spring mechanisms. However, the air compressor or the oil pump required with electro-pneumatic and electro-hydraulic operating mechanisms is an additional component that requires periodic maintenance and is subject to failure.



Figure 22. Example of the stored-energy spring mechanism of a high-voltage, three-pole circuit breaker designed to be used in electric power substations. A single mechanism operates the three interrupter units of the circuit breaker. Three independent mechanisms are sometimes used, one per interrupter unit, in large high-voltage circuit breakers (© Siemens AG 2014, all rights reserved).

1. Trip coil CLOSE

2. Cam plate

3. Corner gear

4. Connecting rod

5. Connecting rod for closing spring

6. Connecting rod for opening spring

7. Closing spring

8. Emergency hand crank

9. Charging gear

10. Charging shaft

11. Roller lever

12. Damper (for closing)

13. Operating shaft

14. Damper (for opening)

15. Trip coil OPEN

16. Operating mechanism housing

17. Opening spring

1

2

3

4

5

6

7

8

9

10

11

12

13

14

15

16

17



Rating of high-voltage circuit breakers

Table 2 provides the main specifications of a typical high-voltage circuit breaker designed to be used in electric power substations.

Table 2. Specifications of a 300 kV circuit breaker.

Parameter description Value

Rated voltage 300 kV

Rated power-frequency withstand voltage 460 kV

Rated lightning-impulse withstand voltage 1050 kV

Maximum, rated normal current 4 kA

Maximum, rated short-time withstand current (1 s to 3 s) 40 kA

Maximum, rated short-circuit breaking current 40 kA

Rated break time 3 cycles

Rated frequency 50 Hz or 60 Hz

Each parameter in Table 2 is briefly described below:

Rated voltage: Voltage at which the circuit breaker is designed to operate (300 kV in this case).

Rated power-frequency withstand voltage: Indicates that the circuit breaker can sustain voltage at the rated power frequency up to a value of 460 kV.

Rated lightning-impulse withstand voltage: Indicates that the circuit breaker can sustain overvoltage caused by lightning up to a value of 1050 kV.

Maximum, rated normal current: Maximum current (4 kA in this case) which the circuit breaker can carry continuously.

Maximum, rated short-time withstand current: Maximum current (40 kA in this case) which the circuit breaker can carry for a short time (1 s to 3 s in this case).

Maximum, rated short-circuit breaking current: Maximum current (40 kA in this case) which the circuit breaker can interrupt.

Rated break time: Time (3 cycles of the ac power source voltage in this case) which the circuit breaker takes to interrupt current.

Rated frequency: Frequency at which the circuit breaker is designed to operate (50 Hz or 60 Hz in this case).

Exercise 1 – High-Voltage Disconnecting Switches and Circuit Breakers Procedure Outline


Cost

High-voltage circuit breakers are the most expensive type of switchgear found in electric power substations. The high cost of high-voltage circuit breakers is largely due to the rapid arc-extinction ability required to quickly interrupt current in a circuit when opening the circuit breaker main contacts.

The Procedure is divided into the following sections:

Set up and connections

Operation of the disconnecting switches

Operation of the circuit breakers

High voltages are present in this laboratory exercise. Do not make or modify any

banana jack connections with the power on unless otherwise specified.

Set up and connections

In this section, you will set up the equipment to observe the operation of disconnecting switches in an electric power substation.

1. Refer to the Equipment Utilization Chart in Appendix A to obtain the list of equipment required to perform this exercise.

Install the required equipment in the Workstation.

2. Make sure that the ac and dc power switches on the Power Supply are set to the O (off) position, then connect the Power Supply to a three-phase ac power outlet.

Make sure that the power switch on the DC Power Supply/Ethernet Switch is set to the O (off) position, then connect the Power Input to an ac power outlet.

Connect the Power Input of the Data Acquisition and Control Interface to a 24 V ac power supply. Turn the 24 V ac power supply on.

3. Connect the USB port of the Data Acquisition and Control Interface to a USB port of the host computer.

PROCEDURE OUTLINE

PROCEDURE

Exercise 1 – High-Voltage Disconnecting Switches and Circuit Breakers Procedure


4. Turn the host computer on, then start the LVDAC-EMS software.

In the LVDAC-EMS Start-Up window, make sure that the Data Acquisition and Control Interface is detected. Make sure that the Computer-Based Instrumentation function for the Data Acquisition and Control Interface is available. Select the network voltage and frequency that correspond to the voltage and frequency of your local ac power network, then click the OK button to close the LVDAC-EMS Start-Up window.

5. Connect the equipment as shown in Figure 23. Use one phase of the three-phase ac power source in the Power Supply to implement the ac power source. Use the 120 V dc output of the DC Power Supply/Ethernet Switch to implement the 120 V dc power source. E1, E2, and E3 are voltage inputs of the Data Acquisition and Control Interface (DACI).

a Motor-operated disconnecting switches are emulated in the Circuit Breakers and Disconnecting Switches 1. However, the symbol representing a manually operated disconnecting switch is used on the front panel of the module due to the lack of space. Also, single-line diagrams are used on the front panel of the module.

Figure 23. Equipment setup used to observe the operation of the disconnecting switches.

Circuit Breakers and Disconnecting Switches 1

DS1-C

Power input 120 V

L

N

I

O

M

E1

E2 E3



6. In LVDAC-EMS, open the Metering window. Set one meter to measure the switched ac power source voltage (i.e., the ac power source voltage measured after the main contacts of disconnecting switch DS1-C using input E1). Set a second meter to measure the dc voltage across the normally-closed auxiliary contact of disconnecting switch DS1-C (measured using input E2). Set a third meter to measure the dc voltage across the normally-open auxiliary contact of disconnecting switch DS1-C (measured using input E3).

Operation of the disconnecting switches

In this section, you will measure voltages using the Data Acquisition and Control Interface and observe LEDs on the Circuit Breakers and Disconnecting Switches 1 to see what happens to the state of the main and auxiliary contacts of disconnecting switch DS1-C when the close (I) and open (O) push buttons of this disconnecting switch are depressed. You will determine how much time the main contacts of disconnecting switch DS1-C take to change state. You will momentarily apply a voltage to the close (I) and open (O) control inputs of disconnecting switch DS1-C to confirm that these inputs can be used to control disconnecting switch DS1-C, just like the push buttons. Finally, you will demonstrate that all disconnecting switches on the Circuit Breakers and Disconnecting Switches 1 module operate like disconnecting switch DS1-C.

7. On the Power Supply, turn the ac power source on.

Turn the DC Power Supply/Ethernet Switch on by setting its power switch to the I (on) position.

8. In the Metering window, measure the switched ac power source voltage. Are the main contacts of disconnecting switch DS1-C open?

9. In the Metering window, measure the dc voltage across each of the two auxiliary contacts of disconnecting switch DS1-C. What is the state of each of these two auxiliary contacts?

Notice that the red (O) LED connected to the normally-closed auxiliary contact of disconnecting switch DS1-C is lit. What does this LED indicate when it is lit?



10. On the Circuit Breakers and Disconnecting Switches 1, momentarily depress the DS1-C close (I) push button in the Circuit Breaker and Disconnecting Switch Control section and observe that the switched ac power source voltage changes after a few seconds.

Measure the switched ac power source voltage. Are the main contacts of disconnecting switch DS1-C closed?

How much time does it take for the main contacts of disconnecting switch DSC1-C to change state?

11. Measure the dc voltage across each of the two auxiliary contacts of disconnecting switch DS1-C. What is the state of each of these two auxiliary contacts?

Notice that the green (I) LED connected to the normally-open auxiliary contact of disconnecting switch DS1-C is lit. What does this LED indicate when it is lit?

12. On the Circuit Breakers and Disconnecting Switches 1, momentarily depress the DS1-C open (O) push button in the Circuit Breaker and Disconnecting Switch Control section and observe that the switched ac power source voltage changes immediately.

Measure the switched ac power source voltage. Are the main contacts of disconnecting switch DS1-C open?



a The next two manipulations require you to observe several events taking place in a relatively short time interval. You can repeat these two manipulations as many times as necessary to validate your observations.

13. On the Circuit Breakers and Disconnecting Switches 1, momentarily depress the DS1-C close (I) push button. Observe the switched ac power source voltage, the dc voltage across each of the two auxiliary contacts of disconnecting switch DS1-C, as well as the red (O) and green (I) LEDs connected to these auxiliary contacts.

Describe what happens when the DS1-C close (I) push button is depressed momentarily.

14. On the Circuit Breakers and Disconnecting Switches 1, momentarily depress the DS1-C open (O) push button and observe the switched ac power source voltage, the dc voltage across each of the two auxiliary contacts of disconnecting switch DS1-C, as well as the red (O) and green (I) LEDs connected to these auxiliary contacts.

Describe what happens when the DS1-C open (O) push button is depressed momentarily.



15. From the observations you made in the two previous steps, what is the state of each of the auxiliary contacts of disconnecting switch DS1-C when this switch changes state (i.e., when disconnecting switch DS1-C is in the in-transit state)? Also, what are the states of the red (O) and green (I) LEDs connected to these auxiliary contacts when disconnecting switch DS1-C changes state?

The next two manipulations require you to make a connection while the

equipment is powered. To minimize the risk of electric shocks, make

sure that you use a safety banana plug lead to make the connection.

16. Connect one end of a safety banana plug lead to the positive (+) terminal of the 120 V dc power source. Momentarily connect the other end of this lead to the DS1-C close (I) control input to apply a voltage pulse to this control input. Describe what happens.

17. Momentarily connect the free end of the lead connected to the positive (+) terminal of the 120 V dc power source to the DS1-C open (O) control input to apply a voltage pulse to this control input. Describe what happens.

Disconnect the end of the lead connected to the 120 V dc power source (i.e., the lead that you used to apply a voltage pulse to the DS1-C control inputs), and return this lead to its storage location.

18. On the Circuit Breakers and Disconnecting Switches 1, successively operate the other disconnecting switches using the corresponding open (O) and close (I) push buttons in the Circuit Breaker and Disconnecting Switch Control section. While doing so, observe that each of these disconnecting switches operates the same way as disconnecting switch DS1-C. Also, observe that each of these disconnecting switches is provided with a red (O) LED and a green (I) LED to indicate the state of its main contacts (open, close, or in transit). However, due to the lack of space on the front panel of the module, no terminals provide access to the auxiliary contacts of each of these disconnecting switches.



19. On the Power Supply, turn the ac power source off.

Turn the DC Power Supply/Ethernet Switch off by setting its power switch to the O (off) position.

Operation of the circuit breakers

In this section, you will measure voltages using the Data Acquisition and Control Interface and observe LEDs on the Circuit Breakers and Disconnecting Switches 1 to see what happens to the state of the main and auxiliary contacts of circuit breaker CB1 when the close (I) and open (O) buttons of this circuit breaker are depressed. You will observe that the main contacts of circuit breaker CB1 change state almost instantaneously. You will momentarily apply a voltage to the close (I) and open (O) control inputs of circuit breaker CB1 to confirm that these inputs can be used to control circuit breaker CB1, just like the push buttons. Finally, you will demonstrate that all circuit breakers on the Circuit Breakers and Disconnecting Switches 1 module operate like circuit breaker CB1.

20. Connect the equipment as shown in Figure 24. Use one phase of the three-phase ac power source in the Power Supply to implement the ac power source. Use the 120 V dc output of the DC Power Supply/Ethernet Switch to implement the 120 V dc power source. E1, E2, and E3 are voltage inputs of the Data Acquisition and Control Interface (DACI).

Figure 24. Equipment setup used to observe the operation of the circuit breakers.

Circuit Breakers and Disconnecting Switches 1

CB1

120 V

L

N

DS1-BDS1-A

E1

E2 E3



21. Make sure that the Power Input of the Circuit Breakers and Disconnecting Switches 1 is connected to the 120 V output of the DC Power Supply/Ethernet Switch.

22. In the Metering window, make sure that one meter is set to measure the switched ac power source voltage (i.e., the ac power source voltage measured after the main contacts of circuit breaker CB1). Make sure that a second meter is set to measure the dc voltage switched by the normally-closed auxiliary contact of circuit breaker CB1 (measured using input E2). Make sure that a third meter is set to measure the dc voltage switched by the normally-open auxiliary contact of circuit breaker CB1 (measured using input E3).

23. On the Power Supply, turn the ac power source on.

Turn the DC Power Supply/Ethernet Switch on by setting its power switch to the I (on) position.

24. On the Circuit Breakers and Disconnecting Switches 1, momentarily depress the DS1-A close (I) push button and the DS1-B close (I) push button. After a few seconds, the green (I) LEDs of disconnecting switches DS1-A and DS1-B should light up.

25. Measure the switched ac power source voltage. Are the main contacts of circuit breaker CB1 open?

26. Measure the dc voltage switched by each of the two auxiliary contacts of circuit breaker CB1. What is the state of each of these two auxiliary contacts?

27. Observe the front panel of the Circuit Breakers and Disconnecting Switches 1. Notice that circuit breaker CB1 is provided with a red (O) LED and a green (I) LED. These LEDs are connected to another set of normally-open and normally-closed auxiliary contacts (not shown on the front panel of the module due to the lack of space) of circuit breaker CB1 in the same way as the LEDs indicating the state of the disconnecting switches (refer to disconnecting switch DS1-C).



Notice that the red (O) LED of circuit breaker CB1 is lit. What does this LED indicate when it is lit?

28. On the Circuit Breakers and Disconnecting Switches 1, momentarily depress the CB1 close (I) push button in the Circuit Breaker and Disconnecting Switch Control section while observing the switched ac power source voltage, the dc voltage switched by each of the auxiliary contacts of circuit breaker CB1, as well as the red (O) and green (I) LEDs of circuit breaker CB1.

29. Measure the switched ac power source voltage. Are the main contacts of circuit breaker CB1 closed?

Does circuit breaker CB1 respond instantaneously to the close command?

Yes No

30. Measure the dc voltage switched by each of the two auxiliary contacts of circuit breaker CB1. What is the state of each of these two auxiliary contacts?

31. Observe the front panel of the Circuit Breakers and Disconnecting Switches 1. Notice that the green (I) LED of circuit breaker CB1 is lit. What does this LED indicate when it is lit?

32. On the Circuit Breakers and Disconnecting Switches 1, momentarily depress the CB1 open (O) push button in the Circuit Breaker and Disconnecting Switch Control section while observing the switched ac power source voltage, the dc voltage switched by each of the auxiliary contacts of circuit breaker CB1, as well as the red (O) and green (I) LEDs of circuit breaker CB1.

Does circuit breaker CB1 respond instantaneously to the open command?

Yes No



33. Observe the front panel of the Circuit Breakers and Disconnecting Switches 1. Notice that circuit breaker CB1 is provided with a yellow (READY) LED. When lit, this LED indicates that circuit breaker CB1 is ready to close, i.e., that energy is stored in the primary (closing) spring of its operating mechanism.

a The operating mechanism of each circuit breaker in the Circuit Breakers and Disconnecting Switches 1 has an energy-storage time (closing spring recompression time) of about 5 s.

Is circuit breaker CB1 ready to close?

34. On the Circuit Breakers and Disconnecting Switches 1, momentarily depress the CB1 close (I) push button to close the main contacts of circuit breaker CB1. Observe the yellow (READY) LED of circuit breaker CB1 at the instant you depress the CB1 close (I) push button, then continue to observe this LED for about 10 s. You should notice that the yellow (READY) LED of circuit breaker CB1 goes out for about 5 s after the main contacts of circuit breaker CB1 have closed. What does it mean? Explain briefly.

35. On the Circuit Breakers and Disconnecting Switches 1, momentarily depress the CB1 open (O) push button to open the main contacts of circuit breaker CB1. Observe the yellow (READY) LED of circuit breaker CB1 at the instant you depress the CB1 open (O) push button. You should notice that the yellow (READY) LED of circuit breaker CB1 remains lit after the main contacts of circuit breaker CB1 have opened. Briefly explain why the yellow (READY) LED of circuit breaker CB1 remains lit.



36. On the Circuit Breakers and Disconnecting Switches 1, successively depress the CB1 close (I) push button and CB1 open (O) push button momentarily to make circuit breaker CB1 close and then open immediately (i.e., before the READY LED of circuit breaker CB1 lights up again). Is there enough energy stored in the operating mechanism of circuit breaker CB1 to allow one closing-opening cycle? Explain briefly.

37. On the Circuit Breakers and Disconnecting Switches 1, use the CB1 close (I) push button and CB1 open (O) push button to try to make circuit breaker CB1 close, open, and close again as rapidly as possible (i.e., before the READY LED of circuit breaker CB1 lights up again). Describe what happens. Explain briefly.

The next two manipulations require that you make a connection while the

equipment is powered. To minimize electric shock hazards, make sure

that you use a safety banana plug lead to make the connection.

38. Connect one end of a safety banana plug lead to the positive (+) terminal of the 120 V dc power source. Momentarily connect the other end of this lead to the CB1 close (I) control input to apply a voltage pulse to this control input. Describe what happens.

39. Momentarily connect the free end of the lead connected to the positive (+) terminal of the 120 V dc power source to the CB1 open (O) control input to apply a voltage pulse to this control input. Describe what happens.

Exercise 1 – High-Voltage Disconnecting Switches and Circuit Breakers Conclusion


40. On the Circuit Breakers and Disconnecting Switches 1, operate the other two circuit breakers (CB2 and CB3) using the corresponding open (O) and close (I) push buttons in the Circuit Breaker and Disconnecting Switch Control section. Observe that each of these circuit breakers operates the same way as circuit breaker CB1.

41. On the Power Supply, turn the ac power source off.

On the DC Power Supply/Ethernet Switch, turn the 120 V dc power source off.

42. Close LVDAC-EMS, then turn off all the equipment. Disconnect all leads and return them to their storage location.

In this exercise, you became familiar with the operation of the disconnecting switches and circuit breakers in the Circuit Breakers and Disconnecting Switches 1 module. You verified that each disconnecting switch and circuit breaker can be opened or closed manually using push buttons. You also verified that each disconnecting switch and circuit breaker can be opened or closed using remote electric control signals. You saw that each disconnecting switch is provided with a set of auxiliary contacts that indicates the state (open, closed, or in transit) of the disconnecting switch main contacts. Similarly, you saw that each circuit breaker is provided with sets of auxiliary contacts that indicate the state (open or close) of the circuit breaker main contacts. You saw that the auxiliary contacts of a disconnecting switch or a circuit breaker are used to control pilot lights (LEDs) that indicate the state of the device main contacts. Finally, you observed that the amount of energy stored in the operating mechanism of each circuit breaker is sufficient to perform one closing-opening cycle.

1. Explain why disconnecting switches are not designed to make or break significant load currents in circuits, but rather to ensure the safety of the maintenance personnel.

CONCLUSION

REVIEW QUESTIONS

Exercise 1 – High-Voltage Disconnecting Switches and Circuit Breakers Review Questions


2. Describe the relationship between the three possible states of a disconnecting switch and the states of its auxiliary contacts, in accordance with the European practice and with the North American practice.

3. Explain what a high-voltage circuit breaker is by describing its two main functions.

Exercise 1 – High-Voltage Disconnecting Switches and Circuit Breakers Review Questions


4. Explain how a high-voltage circuit breaker works by briefly describing its control system, main contacts, auxiliary contacts, and operating mechanism.

5. Why is a means of ensuring rapid arc extinction an essential feature of any high-voltage circuit breaker?

Documents

Exercise 1 High-Voltage Disconnecting Switches and Circuit ... · PDF filefunctions and operation of high-voltage disconnecting switches and circuit ... High-voltage disconnecting